What was the Allied plan for invading the Japanese home islands called?

The Allied plan for invading the Japanese home islands was called Operation Downfall.

Downfall was a proposed United States and British Empire operation intended to defeat Japan through an invasion of its main islands. It was never carried out because Japan surrendered in August 1945.

The plan had two major stages. Operation Olympic was scheduled to land on southern Kyushu in November 1945. Operation Coronet was planned for spring 1946 and would have targeted the Kanto Plain near Tokyo on Honshu.

Downfall is often confused with Olympic and Coronet, but those were component operations rather than the name of the entire invasion plan. Allied planners expected fierce resistance, and estimates of potential casualties varied widely.